Metal-oxide-semiconductor (MOS) transistor is one of the most important components in modern integrated circuits. The basic structure of the MOS transistor includes a semiconductor substrate, a gate structure formed on the semiconductor substrate, and source and drain doped regions formed in the semiconductor substrate on both sides of the gate structure. In the MOS transistor, a switch signal is generated by applying a voltage on the gate structure to adjust a current in a channel under the gate structure.
The MOS transistor includes an N-type MOS transistor and a P-type MOS transistor. A first metal silicide on the surface of the source and drain doped regions of the N-type MOS transistor desires to be selected with an appropriate material, to enable a low first Schottky barrier between the first metal silicide on the surface of the source and drain doped regions and the source and drain doped regions in the N-type MOS transistor. A second metal silicide on the surface of the source and drain doped regions of the P-type MOS transistor desires to be selected with an appropriate material, to enable a low second Schottky barrier between the second metal silicide on the surface of the source and drain doped regions and the source and drain doped regions in the P-type MOS transistor. Accordingly, to meet requirements of the first Schottky barrier between the first metal silicide and the source and drain doped regions in the N-type MOS transistor and the second Schottky barrier between the second metal silicide and the source and drain doped regions in the P-type MOS transistor, respectively, the first metal silicide in the N-type MOS transistor is made of a material different from the second metal silicide in the P-type MOS transistor.
However, existing methods for fabricating a semiconductor device including the N-type MOS transistor and the P-type MOS transistor is complicated and still needs to be improved. The disclosed device structures and methods are directed to solve one or more problems set forth above and other problems.